Jens Fiala

Development of an Implantable Pulse Oximeter

A long-term implantable photoplethysmographic sensor system is proposed. The system employs an elastic cuff which is directly wrapped around an arterial blood vessel. The optically transparent cuff is equipped with light emitting diodes and a photo transistor including the technology of pulse oximetry. The sensor will permit real-time, continuous monitoring of important vital parameters such as arterial blood oxygen saturation and pulse rate over a long-term period in vivo. We emphasize on the specific requirements for design and instrumentation of the implantable sensor and discuss first in vitro data acquired with that new photonics-based sensor.

An implantable optical blood pressure sensor based on pulse transit time

An implantable sensor system for long-term monitoring of blood pressure is realized by taking advantage of the correlation between pulse transit time and blood pressure. The highly integrated implantable sensor module, fabricated using MEMS technologies, uses 8 light emitting diodes (LEDs) and a photodetector on chip level. The sensor is applied to large blood vessels, such as the carotid or femoral arteries, and allows extravascular measurement of highly-resolved photoplethysmograms. In addition, spectrophotometric approaches allow measurement of hemoglobin derivatives. For the calibration of blood pressure measurements, the sensor system has been successfully implemented in animal models.

Subcutaneous blood pressure monitoring with an implantable optical sensor

We introduce a minimally invasive, implantable system that uses pulse transit time to determine blood pressure. In contrast to previous approaches, the pulse wave is detected by a photoplethysmographic (PPG) signal, acquired with high quality directly on subcutaneous muscle tissue. Electrocardiograms (ECG) were measured with flexible, implantable electrodes on the same tissue. PPG detection is realized by a flat 20 mm x 6 mm optoelectronic pulse oximeter working in reflection mode. The optical sensor as well as the ECG electrodes can be implanted using minimally invasive techniques, with only a small incision into the skin, making long-term monitoring of blood pressure in day-to-day life for high-risk patients possible. The in vivo measurements presented here show that the deviation to intra-arterial reference measurements of the systolic blood pressure in a physiologically relevant range is only 5.5 mmHg, demonstrated for more than 12 000 pulses. This makes the presented sensor a grade B blood pressure monitor.

Implantable sensor for blood pressure determination via pulse transit time

High blood pressure (BP), also known as hypertension, is the most common cardiovascular disease and one of the leading causes of death in industrial countries. Clinical research is looking for a possibility to monitor blood pressure continuously. Standard non-invasive cuff-based BP measurement devices have proven ill-suited for a continuous long-term monitoring as they severely restrain the patients mobility. With conventional intravascular sensors, patients run a very high risk of developing thrombosis. The implantable sensor system for continuous BP measurement presented here avoids this risk since it is positioned at the arterys exterior. This paper shows that BP can be determined by measuring the pulse transit time (PTT) entirely inside the body. In vivo measurements with the sensor attached to a domestic pigs carotid artery have clearly shown that the systolic blood pressure and the estimated PTT correlate. This was verified in the physiological BP range of 94-144 mmHg.

Implantable optical sensor for continuous monitoring of various hemoglobin derivatives and tissue perfusion

A novel implantable optical sensor for continuous long-term monitoring of arterial oxygen saturation and monitoring of tissue perfusion is introduced. The photoplethysmo-graphic multi-wavelength sensor with optoelectronic components mounted onto a flexible substrate and encapsulated in biocompatible silicone is attached to well-perfused intrathoracic tissue or directly onto organ surfaces. A proof-of-principle could be shown by first measurements carried out on custom-developed artificial tissue and by in vivo finger-tip measurements as well as in a domestic pig.

In vivo monitoring of blood oxygenation using an implantable MEMS-based sensor

We present a novel implantable, but extravascular, optical sensor for continuous long-term monitoring of vital medical parameters such as arterial blood oxygen saturation, pulse and respiratory frequencies. The biocompatible sensor uses a silicone-based manufacturing technique. It consists of two elastic silicone stripes that house the optoelectronic devices. These flexible stripes can be wrapped around an arterial blood vessel without constricting the vessel or influencing the blood flow - even at large dilatations of 10 %. In vivo experiments on domestic pigs have shown that real-time measurements with this sensor deliver excellent data.

Miniaturized pulse oximeter sensor for continuous vital parameter monitoring

A miniaturized photoplethysmographic sensor system which utilizes the principle of pulse oximetry is presented. The sensor is designed to be implantable and will permit continuous monitoring of important human vital parameters such as arterial blood oxygen saturation as well as pulse rate and shape over a long-term period in vivo. The system employs light emitting diodes and a photo transistor embedded in a transparent elastic cu. which is directly wrapped around an arterial vessel. This paper highlights the specific challenges in design, instrumentation, and electronics associated with that sensor location. In vitro measurements were performed using an artificial circulation system which allows for regulation of the oxygen saturation and pulsatile pumping of whole blood through a section of a domestic pigs arterial vessel. We discuss our experimental results compared to reference CO-oximeter measurements and determine the empirical calibration curve. These results demonstrate the capabilities of the pulse oximeter implant for measurement of a wide range of oxygen saturation levels and pave the way for a continuous and mobile monitoring of high-risk cardiovascular patients.

Wavelet based data analysis for implantable pulse oximetric sensors

Cardiovascular data recording by implantable sensor modules exhibits a number of advantages over extra-corporeal standard approaches. Implantable sensors feature their benefits in particular for high risk patients suffering from chronic heart diseases, because diagnosis can be combined with therapy in a closed loop system. Nevertheless, the measured photoplethysmographic signals reveal different kinds of noise and artifacts. There are several parametric and non-parametric mathematical techniques that try to achieve optimality and generality in estimating the actual signal out of its noisy representation. The determination of blood oxygen saturation and pulse transit time requires one of these mathematical techniques for gaining the exact position and magnitude of maxima and minima in the photoplethysmograph. A robust wavelet algorithm resolves the difficulties arising from physiological data.